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before 900; Middle English understanden, understonden, Old English understondan; cognate with Dutch onderstaan.

To have a comprehension allows one to "stand upon" it or to take a "stand." It is the "under" part of this word confuses me. There is a suggestion that the root of under could have meant between or among; this doesn't clarify "understand" for me.

For a discussion of the etymology of "understand" see World Wide Words by Michael Quinion at http://www.worldwidewords.org/qa/qa-und1.htm

We will never know;lost in the mists of Time.